This invention relates to a circular clarifier for clarifying sludge containing influents, of the type having an improved skimmer assembly.
Sewage treatment facilities have for some time used circular clarifiers to clarify sludge containing influents. In the clarification process, solids sink to the bottom of the clarifier, where they are removed, and clarified effluent is removed from the upper part of the clarifier. Conventionally, solids at the base of the clarifier are removed with a rotating arm which may include scraper blades either alone or in combination with suction orifices for removing settled solids from the bottom of the clarifier.
Additionally, it is important to remove floating scum from the surface of the liquid in the clarifier to prevent the scum from passing out of the clarifier through the effluent removal means. In the past, such scum has been removed with a skimmer assembly mounted to the rotatable arm to sweep across the surface of liquid in the clarifier. One approach is to mount a scum removal conduit approximately at the liquid level and to use the rotating skimmer assembly to push floating scum into the conduit. In this arrangement, it is conventional to mount the skimmer assembly for vertical movement so that the skimmer assembly can move under the scum removal conduit as the rotating arm rotates past the conduit.
In the past, two basic arrangements have been used for allowing the skimmer assembly to move vertically. The first is a simple pivot arrangement, in which the skimmer blades are mounted on vertically extending arms which are mounted to pivot about a horizontal axis. Both counter weights and flotation elements have been mounted on such pivoting skimmer assemblies to provide a biasing force tending to return the skimmer blades to the raised position. Flotation elements that have been used in the past include sealed boxes containing a foam and having an opening on an upper surface thereof. This opening is sealed with a plug such as a threaded plug, and the effective flotation force can be easily adjusted as desired by altering the amount of liquid in the box.
A second linkage used for skimmer assemblies in the past is a parallelogram linkage. To the knowledge of the inventors, such parallelogram linkages have in the past included two vertical links, one directly under the skimmer blade and the other aligned with the support that interconnects the parallelogram linkage with the rotating arm. In the past, a counterweight has been cantilevered off of one of the intermediate links on the opposite side of the support from the skimmer blade. This arrangement has certain disadvantages. The cantilevered counterweight acts with a moment arm that is substantially smaller than the moment arm for the skimmer blade. With this arrangement the required mass of the counterweight is unnecessarily large, thereby increasing the cost, weight, and size of the skimmer assembly unnecessarily. Furthermore, such counterweights tend to be spaced at some distance from the design surface level of liquid in the clarifier, and they can only be exchanged with difficulty, after the clarifier has been drained or filled with clear water.
Accordingly, it is an object of this invention to provide an improved skimmer assembly for a clarifier of the type described above, which utilizes a parallelogram linkage yet avoids the foregoing problems.